Plant hormones mediated temperature-induced anthocyanin accumulation in blood oranges (Citrus sinensis L. Osbeck)

Anthocyanins are enriched in blood oranges (Citrus sinensis L. Osbeck) in response to external environmental stimulation during postharvest storage, while the role of plant hormones in anthocyanin accumulation in response to low-temperature inducement is still poorly studied. Here, we investigated the anthocyanin profiles and fruit quality of blood oranges treated with different temperatures and then further focused on the mechanisms of plant hormone-mediated anthocyanin biosynthesis induced by low temperatures using proteomics. Total and individual anthocyanins were significantly increased in blood oranges under the low-temperature storage at 8 °C, among which cyanidin 3-glucoside and cyanidin 3-(6″-malonylglucoside) were increased by 6.51 and 6.77 times at the end of storage, respectively. Low temperature effectively delayed the weight loss and maintained the water status. For flavor changes, high levels of sucrose, citric acid, and malic acid were observed in fruits stored at 8 °C, and low temperature delayed the changes of overall volatile flavor compounds, in which aroma-active compounds were closer to those in fresh fruit. The proteomic analysis found that differentially expressed proteins between fruit stored at 8 and 25 °C were enriched in “Phenylalanine metabolism”, “Flavonoid biosynthesis”, “Brassinosteroid biosynthesis” and “Cysteine and methionine metabolism” pathways, indicating that low temperature induced the biosynthesis and signal transduction of brassinosteroids and ethylene (CYP90A1, CYP90C1/D1, CYP92A6, SAMS, ACC oxidase, ETR1), upregulated the expression of anthocyanin-related proteins (PAL, 4CL, CHS1, CHS2, F3′5′H, DFR, ANS, and UFGT), and ultimately promoted anthocyanin accumulation in the postharvest blood oranges.